1. Field of the Invention
The present invention relates to an outline mold useful in the shaping and tempering of large glass sheets to non-uniform shape. More specifically, the present invention relates to using a ring-like member as an outline mold in conjunction with a vacuum mold that engages a glass sheet for shaping to a non-uniform shape incorporating longitudinally spaced portions bent relatively sharply and that releases the sheet after preliminary shaping for deposit onto the ring-like member of suitable shape for transporting the shaped sheet from a shaping station to a cooling area.
2. Description of Technical Background and Patents of Interest
The shaping of large glass sheets to shallow shapes has been accomplished in recent years by a method that involves engaging a heat softened glass sheet by vacuum against a vacuum mold having approximately the shape desired for the glass sheet. The glass is lifted on a shaping mold that engages the non-rectangular outline of the sheet and lifts it into close adjacency to a vacuum mold having a downward facing shaping surface of approximately the curvature desired for the glass sheet. Suction supports the bent glass sheet throughout substantially its entire extent against the downward facing shaping surface of the vacuum mold. The lifting member is lowered to provide space for a ring-like member to move into a position below the vacuum mold. When the ring-like member arrives at the position below the vacuum mold, the bent glass sheet is released and permitted to drop onto the ring-like member. The ring-like member transfers the glass sheet to a cooling station where a temper is imparted by rapid cooling.
The art of bending glass sheets involving the dropping of a shaped glass sheet from a vacuum mold onto a ring-like member is relatively simple to accomplish when the glass is shaped about a gentle curvature or has a uniform radius of curvature. However, when the glass is bent to a non-uniform radius of curvature, it is extremely important that the sharply bent portions defined by the ring-like member be aligned precisely beneath the corresponding sharply bent portions defined by the downward facing surface of the vacuum mold. If the sharply bent portions defined by the vacuum mold are not in proper alignment with the corresponding sharply bent portions defined by the ring-like member, the glass sheet will have end portions of different lengths. If sufficiently different in length, the bent glass sheet is unsuitable for fitting within a frame of the vehicle in which it is to be installed.
Since the vacuum mold is located within the exit end of a furnace or above a hearth block just outside the exit of the furnace, it is subject to continuous exposure to the relatively hot temperature radiated by the furnace or the hearth block during a production run. The ring-like member that transfers the bent glass sheet between the shaping station and the cooling station is alternately exposed to the hot temperature of the furnace, heat-softened glass sheet and hearth block when at the shaping station and to the lower temperature provided by cold blasts of air or other tempering medium at the cooling station. Thus, it is relatively easy to estimate the thermal expansion of the distance between the sharply bent portions of the downward facing surface of the vacuum mold between room temperature at which the vacuum mold is fabricated and the temperature range that the mold attains during a production run. The ring-like member, on the other hand, expands thermally a lesser distance between the sharply bent portions. However, the thermal expansion of the ring-like member during a production run is more difficult to predict that that of the vacuum mold because of the cyclic movement of the ring-like member between the relatively hot shaping station and the relatively cool cooling station. To further complicate the arrangement of the vacuum mold and the outline mold comprising said ring-like member, the glass sheet is transferred from the vacuum mold to the outline mold at an elevated temperature that may differ from major surface to major surface, and contracts to its desired ultimate shape at room temperature throughout its extent and thickness. The glass sheet must meet the customer specifications when checked at room temperature to insure its proper installation into a curved frame of a vehicle that receives the bent, tempered glass sheet.
For reasons just mentioned, it is difficult to compensate the initial distance between sharply bent portions along the ring-like member compared to the corresponding distance along the vacuum mold in order to avoid problems in transferring bent glass from a vacuum mold to a ring-like member of outline configuration. If the distance between the sharply bent portions of the shaping surface defined by the ring-like member onto which the hot glass sheet is dropped is less than the corresponding distance in the vacuum mold from which the hot glass sheet is released, it is difficult to settle the portions of the glass sheet to be bent sharply into the sharply bent regions of the ring-like member. If the distance between the sharply bent regions along the ring-like member are too much longer than the desired dimension for the bent glass sheet to insure that the hot glass sheet settles into the sharply bent regions of the ring-like member, the glass sheet will tend to develop a central portion that is too long. A sheet so bent will fail to fit in the curved frame within which it is to be mounted in the vehicle for installation. Once the relative shape of the vacuum mold and the ring-like member have been established at room temperature based on an improper estimate of the corrections needed for the higher temperatures of the vacuum mold and the cyclic temperature range of the ring-like member, it becomes very difficult to make a change to conform the glass sheet to the desired shape.
Typical prior art molds for bending glass sheets or for bending and tempering glass sheets have included molds having gaps disposed at the center thereof to receive electrodes for heaters within the gaps. U.S. Pat. Nos. 2,176,999 to Miller; 3,762,903 to Hamilton and 3,762,904 to Hamilton et al. disclose molds for bending glass sheets to relatively sharp angles that incorporate gaps to receive electrodes so as not to interfere with the mold shaping functions of the mold. The Hamiltion and Hamilton et al. molds are of the outline type.
U.S. Pat. No. 2,857,713 to Cleminson discloses outline molds that are provided at their center and also supported for pivoting at points intermediate the center and ends of the mold so that when a glass sheet softens, a pair of shaping rails pivot into a continuous closed mold position to define the outline of a glass sheet to be bent. The heat softened glass sheet supported on the mold drops to conform to the shape of the mold.
U.S. Pat. No. 2,977,719 to Devore discloses a split type of outline bending mold in which one of a pair of shaping rail sections is pivotally mounted on inner and outer hinges while the other split rail section is rigidly supported on a mold support structure. A glass sheet acts as a strut between end stops to maintain the rail sections separated until it softens and the hingedly supported section moves toward the other shaping rail section. The movable shaping rail section moves inward and downward during the closing of the mold.
U.S. Pat. No. 2,876,594 to McRoberts et al. discloses a split ring mold of convex elevation having a connection between the split ring portions at the mold center to help modify the angle between the mold portions to support sheets of slightly different elevational configuration.
U.S. Pat. No. 3,484,226 to Golightly discloses an outline mold comprising four rail sections interfitted relative to one another to form different outline shapes.
U.S. Pat. No. 3,741,743 to Seymour discloses a sheet shaping frame comprising inner and outer shaping rails spaced apart and supporting a screen mesh that bridges across the gap between the spaced rails to provide a reinforced lightweight support for the outline of a glass sheet.
U.S. Pat. No. 3,973,943 to Seymour discloses a ring-like member of a low heat transfer material reinforced with a metal rail for conveying shaped glass sheets between a shaping station and a cooling station. This patent also discloses how the ring-like member is supported on rigid reinforcing means forming part of a carriage that transports the ring-like member between the shaping station and the cooling station.
U.S. Pat. No. 4,119,428 to DeAngelis et al. discloses an outline bending mold of the gravity sag type having a plurality of split sections extending in end-to-end relation around the perimeter of the mold. Means is provided to adjust each of the sections locally in a direction transverse to the outline shape to modify the outline shape near each split.
U.S. Pat. No. 4,185,986 to Frank and 4,331,464 to Claassen et al. disclose as open ended ring-like member having a split leading edge portion for use with glass sheet bending apparatus that incorporates a vacuum mold. The split in the leading edge portion facilitates moving the downstream end of the ring-like member relative to means that remove the glass sheet from the ring-like member. The split ring-like members of these patents are not adjustable in length.
U.S. Pat. No. 4,252,552 to Frank discloses apparatus for shaping and tempering glass sheets that comprises a vacuum mold of a given shape that engages a heat-softened glass sheet by vacuum to develop a shape conforming to that of the vacuum mold and releases the shaped glass sheet to drop by gravity onto an outline ring-like member that defines a shape of the same or different radius of curvature. For example, this patent uses a vacuum mold defining a curvature having a radius of 48 inches (122 cm) with ring-like members defining shapes ranging from 43 inches (109 cm) to 60 inches (152 cm). While the apparatus of this patent works well to produce bent glass sheets of shallow curvature in the ranges mentioned and also to form shapes of gradually varying radii of curvature, the apparatus of this patent is not designed to overcome certain problems in shaping glass sheets having sharply bent portions that change radius rapidly to sharp bends having radii less than about 24 inches (60 cm) and even as little as 6 inches ( 15 cm).
While the prior art just discussed comprises split rings, there is no reference of which the inventor is aware showing split ring structure for a ring-like mold having a shaping surface defining spaced sharply bent portions and comprising two separate shaping rails spaced apart to make the mold adjustable in length to provide a variation in the distance between sharply bent portions so that a glass sheet may be transferred from a vacuum mold without hanging up on an outline mold or forming a bend on dropping by impact onto the mold shaping surface that has sharply bent portions spaced too far apart to meet the tolerances required by the customer for acceptable fit within a frame in which the bent window is to be installed.